The principal objective of this project is to develop a computer-based radiation therapy treatment planning program that accounts for tissue heterogeneities and accurately (within plus or minus 5%) computes the dose delivered to patients treated with 6-18 MeV electrons. The program will use computed tomographic data to predict the location, configuration and absorption characteristics of anatomical features of patients being treated. The influence of these features on the absorption and scattering of electrons will be estimated analytically and verified experimentally, leading to development of an algorithm for calculating dose distributions for electron treatments. Calculated dose distributions will be compared to actual dose distributions measured in phantoms to estimate the accuracy of the algorithm in a variety of patient geometries.